A variety of methods for reflow soldering technology to mount electronic components on printed circuit boards are already known. These methods include, for example, batch reflow soldering of surface mount components, local soldering of insert mount components after batch reflow soldering of surface mount components, and local reflow soldering of surface mount components and insert mount components.
A conventional reflow device for batch reflow soldering of surface mount components is constituted so as to melt solder and to solder electronic components by uniformly heating a printed circuit board with the radiant heat of a panel heater and hot air heated to a prescribed temperature.
Also, the reflow device according to the report of Japanese Patent Publication No. 7-73790 is an example of a reflow device for local heating and reflow of surface mount components and insert mount components. As shown in FIG. 11, this reflow device (50) is equipped with the following: hot air chamber (53) installed on the lower side of the transport path (52) for the printed circuit board (51) which collects gas heated to a temperature at which solder cream melts, an upper plate (57) installed to cover the opening section (54) of the hot air chamber (53) and in which is formed a plurality of hot air blow holes (56) to blow the hot air (55) selectively on only the necessary sections of the printed circuit board (51), and means for transport (58) to supply and remove the printed circuit board (51).
Because heating is local, this reflow device (50) makes possible the following processes: sectional soldering, soldering of components with low heat resistance, and concurrent soldering of lead components (59) and chip components (60) wherein the lead terminals protrude from the lower surface of the board.
However, batch reflow soldering is not possible when using the aforementioned, conventional type of reflow device if electronic components with low heat resistance are present together on a printed circuit board. Those components with low heat resistance among the electronic components will be damaged if that printed circuit board undergoes batch reflow soldering with the reflow device; therefore, the components with low heat resistance among the electronic components must be soldered separately, resulting in the problem of decreased productivity of the mounting process.
Meanwhile, the reflow device (50) shown in FIG. 11 makes possible batch soldering for a printed circuit board (51) on which electronic components with low heat resistance are present together by locally blowing hot air without blowing the hot air to the locations of the electronic components with low heat resistance.
Actually, batch soldering of the electronic components (lead component (59) and chip component (60), etc.) placed on the entire surface of the printed circuit board (51) is not possible for the following reason. In effect, reflow soldering electronic components such as lead component (59) and chip component (60), etc., with the reflow device (50) requires heating to temperatures in the vicinity of 230.degree. C. for 20-30 seconds. Hot air of a temperature of roughly 350.degree. C. or greater is necessary to ensure the quantity of heat necessary for that purpose. In hot air of such high temperatures, areas of the printed circuit board (51) in which the temperature rises easily reach temperatures approaching that of the hot air. Even heat resistant components (for example, the temperature of heat resistance for QFP is 250.degree. C. (QFP is heat resistant to temperatures of 250.degree. C.) cannot withstand that temperature. When the hot air temperature is reduced to 250.degree. C., the temperature of heat resistance, in order to avoid [damage], the risk is that areas of the printed circuit board (51) in which the temperature rises with difficulty are not heated to the temperatures necessary for soldering within a prescribed period of time and high reliability soldering may not result.